1. Field of the Invention
The present invention relates to a guide beam direction setting apparatus which aligns the direction of emission of the guide beam emitted from a guide beam generator with the direction of collimation of a survey to prescribe the emission direction of the guide beam, and more particularly to a guide beam direction setting apparatus capable of application to a tunnel digging operation.
2. Description of Related Art
There is a method of tunnel construction which lays pipes, such as Hume concrete pipes and metallic steel pipes, at a position of fixed depth from the ground. As this construction method, there is known an open cut method according to which piping grooves are dug at a position of fixed depth from the ground and pipes are laid. There is also known a dig propulsion method according to which piping tunnels are dug at a place of fixed depth from the ground and pipes are connected in sequence by press fitting. In these construction methods a survey is made in order to determine the direction in which the pipes are laid.
FIG. 1 schematically illustrates a conventional guide beam direction setting apparatus for determining the direction in which the pipe is laid. In the figure, reference numeral 1 denotes a vertical pit, reference numeral 2 a surveying machine, such as a theodolite, installed on the ground surface GL, and reference numeral 3 a surveying machine installed at a place of fixed depth from the ground. The surveying machine 2 is employed as a collimation direction means.
A hanging frame 4 is installed on the ground surface GL as a plumb-bob device. The hanging frame 4 hangs two weights 6 thereon with two suspension wires 5. The two suspension wires 5 are tensioned by the weights 6 so that they become parallel with each other. The weight 6 is immersed into liquid 7, such as oil having a high viscosity, in order to prevent the oscillation of the suspension wire 5, such as lateral and vertical swings.
An operator determines a direction of collimation L in accordance with a pipe laying plan and operates the hanging frame 4 so that the two suspension wires 5 are superimposed and seen as a signal wire. In this way, an imaginary plane including the collimation direction L is formed. For example, a theodolite or a level is employed as the surveying machine 3. The surveying machine 3 adjusts collimation so that the suspension wires 5 are seen as being superimposed. In this way, the collimation direction L as viewed on the ground is aligned with the collimation direction as viewed underground. This collimation direction is assumed to be a digging direction.
Also, if there is provided a guide beam generator which emits a guide beam in a direction aligning with the collimation direction of the surveying machine 3, the digging direction can be prescribed based on the direction of emission of the guide beam. If the digging operation of the tunnel 8 is performed based on the collimation direction of this surveying machine 3 (or the guide beam), pipe laying can be performed according to plans.
However, the conventional direction setting apparatus, where the collimation direction of the surveying machine 3 (or the emission direction of the guide beam) and the collimation direction L are aligned with each other by making use of a plumb-bob device, is on an elaborate scale. In addition, the operation of aligning the collimation direction (or the emission direction of the guide beam) with the collimation direction L takes time. Furthermore, in this conventional direction setting apparatus, the size of the vertical pit 1 is restricted from recent road circumstances and therefore the base length (i.e., interval between two suspension wires 5) cannot be freely enlarged. Therefore, if the copying of the survey is made from the ground surface GL to the pit 1 and from the pit 1 to the tunnel 8, cumulative error will become significant.